University of Oulu

Workayehu, A. B., Vanhamäki, H., & Aikio, A. T. ( 2019). Field‐aligned and horizontal currents in the Northern and Southern Hemispheres from the Swarm satellite. Journal of Geophysical Research: Space Physics, 124, 7231– 7246.

Field‐aligned and horizontal currents in the Northern and Southern Hemispheres from the Swarm satellite

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Author: Workayehu, A. B.1; Vanhamäki, H.1; Aikio, A. T.1
Organizations: 1Ionospheric Physics Research Unit, University of Oulu, Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 4.4 MB)
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Language: English
Published: American Geophysical Union, 2019
Publish Date: 2020-02-07


We present statistical investigation of the high‐latitude ionospheric current systems in the Northern Hemisphere (NH) and Southern Hemisphere (SH) during low (Kp < 2) and high (Kp ≥ 2) geomagnetic activity levels. Nearly 4 years of vector magnetic field measurements are analyzed from the two parallel flying Swarm A and C satellites using the spherical elementary current system method. The ionospheric horizontal and field‐aligned currents (FACs) for each auroral oval crossing are calculated. The distributions of the mean values of FACs as well as the horizontal curl‐free and divergence‐free currents in magnetic latitude and magnetic local time for each hemisphere and activity level are presented. To estimate the NH/SH current ratios for the two activity levels, we remove seasonal bias in the number of samples and in the Kp distribution by bootstrap resampling. This is done in such a manner that there are equal number of samples from each season in each Kp bin. We find that for the low activity level, the currents in the NH are stronger than in the SH by 12±4% for FAC, 9±2% for the horizontal curl‐free current, and 8±2% for the horizontal divergence‐free current. During the high activity level, the hemispheric differences are not statistically significant. This suggests that the local ionospheric conditions, such as magnetic field strength or daily variations in insolation, may be important and play a larger role during quiet than disturbed periods. This issue must be studied further.

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Series: Journal of geophysical research. Space physics
ISSN: 2169-9380
ISSN-E: 2169-9402
ISSN-L: 2169-9380
Volume: 124
Issue: 8
Pages: 7231 - 7246
DOI: 10.1029/2019JA026835
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Copyright information: © 2019. American Geophysical Union.